1. Field of the Invention
The present invention relates to a cooling apparatus, and, in particular, to a cooling apparatus for cooling a semiconductor chip or the like.
2. Description of the Prior Art
Because a heat generating member of a semiconductor chip produces heat during operation the semiconductor chip is cooled by means of a cooling apparatus to maintain a uniform performance.
Conventionally, various types of cooling devices such as those illustrated in FIG. 1 to FIG. 5 are used for cooling a semiconductor chip.
A cooling apparatus for cooling a semiconductor chip shown in FIG. 1 comprises a fin assembly 101 mounted on the upper part of a semiconductor chip 102. A plurality of semiconductor chips 102 is illustrated, each chip attached to a substrate 103. Then, a fluid such as air or the like is caused to flow, by means of a fan 105, through a vessel 104 in which are housed the semiconductor chips 102, bearing the fin assemblies 101, and the substrates 103, to dissipate the heat from the semiconductor chips 102 into the air.
However, with this type of cooling apparatus which cools by the airflow from the fan 105 through the fins 101 mounted on the semiconductor chip 102, when the semiconductor chips are mounted at a high density on the substrate 103, as in contemporary chips, because of the considerable increase in the amount of heat radiated from all the semiconductor chips combined, the problem arises that it is not possible to efficiently cool the semiconductor chips 102 with uniform temperature distribution.
With the cooling apparatus for cooling a semiconductor chip shown in FIG. 2, a plurality of semiconductor chips 111 (three in the drawing) attached to a substrate 112 are positioned within a space 115 formed between a base 113, which bears the substrate 112 on its inner side, and a heat transmitting block 114.
A cooling stud 116 is inserted into a space opened by a hole 114a and contacts the upper portion of the semiconductor chip 111 inside the hole 114a which is formed in the heat transmitting block 114. The cooling stud 116 presses against the semiconductor chip 111 from the action of a string 117 installed in the hole 114a. Also, a channel 118, in which a coolant flows, is formed in the heat transmitting block 114. Helium gas is filled into the space 115 formed between the base 113 and the heat transmitting block 114.
With the conventional types of cooling apparatus described above, the heat produced by the semiconductor chip 111 is transmitted to the cooling stud 116, and is also transmitted to the heat transmitting block 114 through the helium gas. Then, the semiconductor chip 111 is cooled by the cooling of the heat transmitting block 114 from the coolant flowing in the channel 118.
However, with the above-mentioned conventional cooling apparatus, because of poor precision of assembly, in the case where the cooling stud 116 contacts the upper portion of the semiconductor chip 111 at an angle, considerable heat resistance is produced at the point of contact so that the cooling effect is diminished, and, in addition, the heat in the semiconductor chip 111 encounters a large amount of heat resistance in transmitting heat to the heat transmitting block 114 by heat conduction from a gas such as helium.
In the cooling apparatus for cooling a semiconductor chip shown in FIG. 3, a heat transmitting block 122 is thermally connected to the surface of a semiconductor chip 121. On the side of the heat transmitting block 122 opposite to the semiconductor chip 121, a plurality of channels 124 is formed from a plurality of fins 123 arranged linearly (each fin 123 having a cross section of from several tens to seveal hundreds .mu.m square) (see FIG. 4). The fins 123 are formed by an etching process.
The fins 123 on the heat transmitting block 122 are enclosed by a cover plate 125. A feed port 126 is provided on one end of the cover plate 125 and a discharge port 127 on the other for circulating the coolant through the channels 124.
With the above-mentioned conventional cooling apparatus, when heat is produced by the semiconductor chip 121, this heat is transmitted to the fins 123 of the heat transmitting block 122. Then, the fins 123 of the heat transmitting block 122 are cooled by the coolant flowing in the channels 124, thus cooling the semiconductor chip 121.
However, because the fins 123 are formed linearly between the feed port 126 and the discharge port 127 in the above-mentioned conventional cooling apparatus, the heat transfer coefficient of the fins 123 drops, and, in addition, the channel resistance of the channel 124 formed by the fins 123 is large, so that the efficiency of the cooling of the semiconductor chip 121 is reduced.
In the cooling apparatus for cooling a semiconductor chip shown in FIG. 5, a plurality of semiconductor chips 131 (three in the drawing) are attached to a substrate 132, and on the reverse surface of the substrate 132 (the surface opposite the side on which the semiconductor chip is attached in the drawing), a cap 136 for sealing in a working fluid 135 is integrally joined to a pipe section 134, forming a heat pipe. A plurality of fins 133 is attached to the outside of the pipe section 134.
With the above-mentioned conventional cooling apparatus, when heat is produced by the semiconductor chip 131, this heat passes through the substrate 132 and is transmitted to the working fluid 135 contained by the cap 136, thus heating the working fluid 135. The heated working fluid 135 rises inside the pipe section 134 and after the heat is removed by radiation from the fins 133, is liquefied and returns to the cap 136.
However, with the above-mentioned conventional cooling apparatus, when the coefficient of thermal conductivity of the substrate 132 is poor, the problem arises that the heat resistance is large and the heat in the semiconductor chip 131 cannot be effectively transmitted into the working fluid 135 in the cap 136. Therefore, the efficiency of the cooling of the semiconductor chip 121 is reduced.
As outlined above, in the types of cooling apparatus for cooling a semiconductor chip shown in FIG. 1 to FIG. 5, when the semiconductor chips are mounted at a high density and when large amounts of heat are contained, as in contemporary chips, good cooling is not possible.